================================================================================ VHF/UHF REMOTE ELEMENT SWITCHING SYSTEM 6 METERS (50.1 MHz) - RELAY-BASED ELEMENT SWITCHING COMPLETE IMPLEMENTATION FOR 5-ELEMENT YAGI SWITCHING ================================================================================ OVERVIEW ──────── At 6M, SPDT relays are ideal for element control. Contact loss is < 0.15 dB. This document specifies component values, wiring, and PCB layout for complete 5-element yagi with reflector + 3 director switching via 4× DPDT relays. ================================================================================ RELAY MATRIX: 5-ELEMENT YAGI (50.1 MHz) ================================================================================ ELEMENT | Function | Relay Type | Supply ───────────────────────────────────────────────────────────── Reflector | Reflector/Bypass | K1 DPDT | +5V Director 1 | Director/Bypass | K2 DPDT | +5V Director 2 | Director/Bypass | K3 DPDT | +5V Director 3 | Director/Bypass | K4 DPDT | +5V RELAY SWITCHING TABLE (Simplified): Pattern | K1(Refl) | K2(Dir1) | K3(Dir2) | K4(Dir3) | Gain | F/B ─────────────────────────────────────────────────────────────────────────── OMNI (all free) | OFF | OFF | OFF | OFF | ~9 dBd | 20 dB 5-ELEMENT (baseline)| OFF | OFF | OFF | OFF | ~9 dBd | 20 dB 3-ELEMENT COMPACT | OFF | OFF | ON* | ON* | ~6 dBd | 10 dB REVERSE (back) | ON* | OFF | OFF | OFF | ~3 dBd | 8 dB CARDIOID-E | OFF | OFF | OFF | ON* | ~7 dBd | 12 dB * ON = relay energized = relay NC contact open = element free (director) OFF = relay de-energized = relay NC contact closed = element shorted (reflector) ================================================================================ COMPONENT SPECIFICATIONS ================================================================================ Relays (K1, K2, K3, K4): ───────────────────── Part: Omron G5V-2-5 (DPDT, 5V coil, 40 mA, gold-plated contacts) Packaging: Plug-in 8-pin DIL package Coil Voltage: 5V DC Coil Resistance: ~125 Ω Coil Power: 0.2 W typical Contact Rating: 2A @ 30V DC (more than sufficient) Contact Bounce: ~1 ms Isolation: > 40 dB RF Loss @ 50 MHz: < 0.15 dB RF Loss @ 144 MHz:< 0.25 dB Cost: $1.50-2.50 per relay (Digi-Key, Mouser, etc.) Total for 4 relays: $6-10 Driver IC (U1): ────────────── Part: Texas Instruments ULN2803 (Darlington Array, 8-channel) Function: Convert 3V3 ESP32 GPIO to 5V relay drive current Pin configuration: 18-pin DIP Max output current: 500 mA per channel (sufficient for 4× relays @ 40 mA each) Max total current: 2.7 A (all channels) Flyback protection: Built-in (integrated catch diodes) Cost: $0.30-0.50 per IC Power Supply: ───────────── Relay coil supply: +5V DC @ 200 mA (4 relays × 40 mA + margin) Source: Separate regulated 5V from wall supply OR boost from 12V buck Decoupling: 1000 µF electrolytic + 100 nF ceramic across +5V rail Control Signals (from ESP32): ──────────────────────────── GPIO2 → ULN2803 Input 1 → K1 (Reflector) GPIO4 → ULN2803 Input 2 → K2 (Director 1) GPIO5 → ULN2803 Input 3 → K3 (Director 2) GPIO17 → ULN2803 Input 4 → K4 (Director 3) Input impedance: ~1 MΩ (standard CMOS logic, 3V3 levels acceptable) Max input frequency: > 10 kHz (relays are slow, ~100 Hz switching sufficient) ================================================================================ DETAILED SCHEMATIC: SINGLE RELAY CIRCUIT ================================================================================ ESP32 GPIO2 (3V3 output) │ o─────────[R_1k]─────┐ 1 kΩ │ ±5% │ │ GND ──────────────────────┴─→ ULN2803 IN(1) (pin 1, 18-pin DIP) ULN2803 OUTPUT (pin 16): +5V relay supply │ ┌──o──────────┐ │ │ [K1_coil] [K1] │ ├─ Pin 2: COM (connected to element) │ ├─ Pin 3: NO (connected to nothing) │ └─ Pin 8: NC (connected to boom GND) │ (When coil ON: COM to NO path open, element free = director) │ (When coil OFF: COM to NC path closed, element shorted to boom) │ [Flyback 1N4007] ← Built-in to ULN2803, no external needed │ ULN2803 Output 1 (pin 16) │ Common ─────→ Pin 9 (COM of ULN2803) │ GND ================================================================================ RELAY WIRING: ELEMENT-TO-BOOM SHORTING CONFIGURATION ================================================================================ For a single parasitic element (e.g., Director 1): Element Center Feed Point (from boom) │ [C_iso 1 µF] ← Isolate DC from boom │ o─────────┬──── To coax connector (towards receiver/amp) │ [K2 relay] ← Omron G5V-2-5 │ K2-PIN2 (COM) ← element input K2-PIN3 (NO) ← Unused/open circuit K2-PIN8 (NC) ← Connected to boom RF ground When K2 relay is OFF (not energized): Element connects through K2-NC to boom, acts as shorted stub (reflector) When K2 relay is ON (energized via ULN2803): Element is isolated (NO path is open), acts as free director ================================================================================ PCB LAYOUT (Single-sided OR two-sided FR-4, 50 mil trace minimum) ================================================================================ Layout strategy: Minimize relay coil lead length (< 50 mm total) Separate analog and digital grounds, merge at single star point LAYER 1 (Top): ────────────── ┌─────────────────────────────────────────────────┐ │ │ │ ╔═══════════════════════════════════════════╗ │ │ ║ ULN2803 IC (U1) ║ │ │ ║ Input pins 1-4: from ESP32 GPIO via 1k Ω ║ │ │ ║ Output pins: to relay coils ║ │ │ ║ PIN 9 (COM): to GND plane ║ │ │ ╚═══════════════════════════════════════════╝ │ │ │ │ │ │ │ │ │ │ │ │ │ │ [K1] [K2] [K3] [K4] (Relay modules) │ │ │ │ │ │ │ │ └──────┴──────┴──────┘ │ │ │ │ │ GND PLANE (continuous) │ │ │ └─────────────────────────────────────────────────┘ LAYER 2 (Bottom): ───────────────── Solid ground plane (connected to via grid) Power and signal traces use top layer Power Distribution: ─────────────────── +5V comes from separate power supply (or 12V buck converter) 1000 µF bulk cap + 100 nF ceramic at ULN2803 Vcc pin Relay coils connect to +5V via ULN2803 outputs Via Placement: ────────────── Ground vias every ~10 mm in GND plane Power vias under each relay coil (< 5 mm) ================================================================================ CONNECTOR PINOUT (DB9 Control Interface) ================================================================================ Control Connector (male DB9, facing outward): PIN SIGNAL | Description ───────────────────────────────────── 1 +12V (aux) | Optional 12V supply for future expansion 2 GPIO2 (K1) | Reflector relay control 3 GPIO4 (K2) | Director 1 relay control 4 GPIO5 (K3) | Director 2 relay control 5 GPIO17 (K4) | Director 3 relay control 6 GND | Ground reference 7 +5V (relay) | 5V relay supply (local, on PCB) 8 SPARE | Future use 9 GND (return) | Ground return, shield connection Shielded cable from ESP32 to relay box (>1m): Ferrite bead on each signal line ================================================================================ FIRMWARE PSEUDO-CODE (Arduino, ESP32) ================================================================================ // GPIO assignments #define RELAY_REFL GPIO_NUM_2 #define RELAY_DIR1 GPIO_NUM_4 #define RELAY_DIR2 GPIO_NUM_5 #define RELAY_DIR3 GPIO_NUM_17 // Pattern definitions enum Pattern { OMNI, BASELINE_5EL, COMPACT_3EL, REVERSE, CARDIOID_E, // ... more patterns }; void setPattern(Pattern p) { // Step 1: De-energize all relays (all elements shorted = reflector mode) gpio_set_level(RELAY_REFL, LOW); gpio_set_level(RELAY_DIR1, LOW); gpio_set_level(RELAY_DIR2, LOW); gpio_set_level(RELAY_DIR3, LOW); delay(50); // Wait for contact settling // Step 2: Apply pattern-specific GPIO states switch(p) { case BASELINE_5EL: // All directors free (OFF state) gpio_set_level(RELAY_DIR1, LOW); gpio_set_level(RELAY_DIR2, LOW); gpio_set_level(RELAY_DIR3, LOW); break; case COMPACT_3EL: // Dir 2 & 3 shorted, Dir 1 free gpio_set_level(RELAY_DIR1, LOW); gpio_set_level(RELAY_DIR2, HIGH); // Shorted gpio_set_level(RELAY_DIR3, HIGH); // Shorted break; // ... more patterns } delay(50); // Wait for settle updateSWR(); // Check via NanoVNA or RF sensor } ================================================================================ TESTING & COMMISSIONING ================================================================================ 1. VISUAL INSPECTION: ───────────────── - All solder joints clean and shiny - No bridges between traces - Relay coil leads securely soldered 2. CONTINUITY TEST (with ohmmeter): ──────────────────────────────── - NC contact (when relay OFF): should be ~ 0.5 Ω - NO contact (when relay ON): should be open (> 10 MΩ) - Repeat for all 4 relays 3. VOLTAGE TEST (with multimeter): ────────────────────────────── - +5V rail: should be 5.0 ± 0.2V when relays OFF - Relay coil voltage when ON: should be 4.9 V (drop across ULN2803) 4. PATTERN VERIFICATION (at antenna): ────────────────────────────────── - Connect to NanoVNA, measure S11 at driven element - Apply each pattern via ESP32 WebUI - Verify SWR changes appropriately - Measure antenna pattern with field strength meter or satellite doppler ================================================================================ PARTS LIST (6M System, 5-Element Array) ================================================================================ Qty Part Number | Description | Value | Cost ──────────────────────────────────────────────────────────────── 4 Omron G5V-2-5 | Relay DPDT 5V | 40 mA | $2.00 each 1 ULN2803APC | Darlington Array IC | 8-channel | $0.40 1 1N4007 | Flyback diode | 1A/1kV | $0.05 1 C315C105M5U | Capacitor, isolation | 1 µF/50V | $0.15 4 100 nF 0402 | Capacitor, bypass | 100 nF | $0.02 each 1 1000 µF electrolytic| Capacitor, bulk | 1000 µF | $0.20 1 DB9M connector | Control interface | 9-pin | $0.30 4 1 kΩ ±5% resistors | Input base resistors | 1/4 W | $0.02 each 1 PCB blank (2"x2") | Single-sided FR-4 | 50 mil | $1.00 1 4-pin JST header | Element feed pigtail | 2.54mm | $0.10 TOTAL COMPONENT COST: ~$12-15 per array ================================================================================ RELATED DOCUMENTS ================================================================================ - relay_switching_ascii.txt: General relay switching overview - yagi_6m_baseline_5el.nec: NEC2 antenna model - yagi_6m_reversible_3el.nec: Reversible yagi model - rf_isolation_filter_ascii.txt: Control line EMI filtering